Sensor with in-stack bias structure providing exchange stabilization

ABSTRACT

A magnetic head having an in-stack bias structure and a free layer structure. The in-stack bias structure includes an antiferromagnetic layer; a first bias layer positioned towards the antiferromagnetic layer, a magnetic moment of the first bias layer being pinned by the antiferromagnetic layer; a first antiparallel coupling layer positioned adjacent the first bias layer; and a second bias layer positioned between the first and second antiparallel coupling layers and having a magnetic moment pinned antiparallel to the magnetic moment of the first bias layer. A second antiparallel coupling layer is positioned adjacent the second bias layer of the bias structure. The free layer structure, positioned adjacent the antiparallel coupling layer, includes a first free layer having a magnetic moment and a second free layer having a magnetic moment pinned antiparallel to the magnetic moment of the first free layer. The second bias layer is antiparallel coupled to the first free layer of the free layer structure for stabilizing the free layer structure.

FIELD OF THE INVENTION

The present invention relates to magnetic heads, and more particularly,this invention relates to magnetic sensors having an in-stack biasstructure providing exchange stabilization.

BACKGROUND OF THE INVENTION

The heart of a computer is a magnetic disk drive which includes arotating magnetic disk, a slider that has read and write heads, asuspension arm above the rotating disk and an actuator arm that swingsthe suspension arm to place the read and write heads over selectedcircular tracks on the rotating disk. The suspension arm biases theslider into contact with the surface of the disk when the disk is notrotating but, when the disk rotates, air is swirled by the rotating diskadjacent an air bearing surface (ABS) of the slider causing the sliderto ride on an air bearing a slight distance from the surface of therotating disk. When the slider rides on the air bearing the write andread heads are employed for writing magnetic impressions to and readingmagnetic signal fields from the rotating disk. The read and write headsare connected to processing circuitry that operates according to acomputer program to implement the writing and reading functions.

In high capacity disk drives, magnetoresistive (MR) read sensors,commonly referred to as MR heads, are the prevailing read sensorsbecause of their capability to read data from a surface of a disk atgreater track and linear densities than thin film inductive heads. An MRsensor detects a magnetic field through the change in the resistance ofits MR sensing layer (also referred to as an “MR element”) as a functionof the strength and direction of the magnetic flux being sensed by theMR layer.

The conventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which an MR element resistance variesas the square of the cosine of the angle between the magnetization inthe MR element and the direction of sense current flow through the MRelement. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in the direction of magnetization of the MRelement, which in turn causes a change in resistance of the MR elementand a corresponding change in the sensed current or voltage.

Another type of MR sensor is the giant magnetoresistance (GMR) sensormanifesting the GMR effect. In GMR sensors, the resistance of the GMRsensor varies as a function of the spin-dependent transmission of theconduction electrons between ferromagnetic layers separated by anon-magnetic layer (spacer) and the accompanying spin-dependentscattering which takes place at the interface of the ferromagnetic andnon-magnetic layers and within the ferromagnetic layers.

GMR sensors using only two layers of ferromagnetic material (e.g.,Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) aregenerally referred to as spin valve (SV) sensors. In an SV sensor, oneof the ferromagnetic layers, referred to as the pinned layer (referencelayer), has its magnetization typically pinned by exchange coupling withan antiferromagnetic (e.g., NiO or Fe—Mn) layer. The pinning fieldgenerated by the antiferromagnetic layer should be greater thandemagnetizing fields (about 200 Oe) at the operating temperature of theSV sensor (about 120° C.) to ensure that the magnetization direction ofthe pinned layer remains fixed during the application of external fields(e.g., fields from bits recorded on the disk). The magnetization of theother ferromagnetic layer, referred to as the free layer, however, isnot fixed and is free to rotate in response to the field from therecorded magnetic medium (the signal field). U.S. Pat. No. 5,206,590granted to Dieny et al., incorporated herein by reference, discloses aSV sensor operating on the basis of the GMR effect.

An exemplary high performance read head employs a spin valve sensor forsensing the magnetic signal fields from the rotating magnetic disk. FIG.1 shows a prior art SV sensor 100 comprising a free layer (freeferromagnetic layer) 110 separated from an in-stack biasing layer(pinned ferromagnetic layer) 120 by a non-magnetic,electrically-conducting spacer layer 115. The magnetization of thebiasing layer 120 is fixed by an antiferromagnetic (AFM) layer 130. Thebiasing layer 120 stabilizes the free layer.

FIG. 2 shows another prior art SV sensor 150 with a flux keeperedconfiguration. The SV sensor 150 is substantially identical to the SVsensor 100 shown in FIG. 1 except for the addition of a keeper layer 152formed of ferromagnetic material separated from the free layer 110 by anon-magnetic spacer layer 154. The keeper layer 152 provides a fluxclosure path for the magnetic field from the pinned layer 120 resultingin reduced magnetostatic interaction of the pinned layer 120 with thefree layer 110. U.S. Pat. No. 5,508,867 granted to Cain et al.,incorporated herein by reference, discloses a SV sensor having a fluxkeepered configuration.

One problem encountered in such structures is that the singleferromagnetic biasing layer 120 must be as thick as the free layer 110in order to provide sufficient stabilization. However, when a biasinglayer 120 of such large thickness is used, the coupling of the AFM 130to the ferromagnetic biasing layer 120, being inversely proportional tothickness, results in poorly pinned biasing layer 120. The result is apoorly stabilized free layer 120.

What is needed is a way to increase the AFM coupling to an in-stackbiasing layer, thereby stabilizing the in-stack biasing layer.

What is also needed is a new in-stack biasing structure that providesgood stabilization of the free layer.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks and limitations describedabove by providing a magnetic head. The head includes an in-stack biasstructure and a free layer structure. The in-stack bias structureincludes an antiferromagnetic layer; a first bias layer positionedtowards the antiferromagnetic layer, a magnetic moment of the first biaslayer being pinned by the antiferromagnetic layer; a first antiparallelcoupling layer positioned adjacent the first bias layer; and a secondbias layer positioned between the first and second antiparallel couplinglayers and having a magnetic moment pinned antiparallel to the magneticmoment of the first bias layer. A second antiparallel coupling layer ispositioned adjacent the second bias layer of the bias structure. Thefree layer structure, positioned adjacent the antiparallel couplinglayer, includes a first free layer having a magnetic moment and a secondfree layer having a magnetic moment pinned antiparallel to the magneticmoment of the first free layer. The second bias layer is antiparallelcoupled to the first free layer of the free layer structure forstabilizing the free layer structure.

In one embodiment, a net magnetic thickness of the first and second biaslayers is greater than zero for providing magnetostatic stabilization ofthe free layer structure in addition to the exchange stabilizationprovided by the antiparallel coupling of the second bias layer and thefirst free layer. A preferred net magnetic thickness of the first andsecond bias layers is less than about 20 Å, the thickness being measuredin a direction perpendicular to a plane of the first free layer. Thefirst bias layer preferably has a larger magnetic thickness than thesecond bias layer.

In a preferred embodiment, a thickness of the second antiparallelcoupling layer is greater than a thickness of the first antiparallelcoupling layer. A preferred thickness of the second antiparallelcoupling layer is about 16 Å to about 20 Å.

In a further embodiment, the second free layer has a larger magneticthickness than the first free layer.

The head preferably further includes an antiparallel (AP) pinned layerstructure positioned towards the free layer structure on an oppositeside of the free layer structure relative to the bias structure. The APpinned layer structure has at least two pinned layers having magneticmoments that are self-pinned antiparallel to each other. The AP pinnedlayer structure further stabilizes the free layer structure. To furtherenhance the pinning of the AP pinned layer structure, at least oneantiferromagnetic (AFM) layer can be positioned towards the AP pinnedlayer structure.

The head may also include shield layers positioned above and below thefree layer structure. To further reduce the effects of side reading fromadjacent tracks, portions of the shield layer positioned outside thetrack edges can be made to extend downwardly towards the portions of thefree layer structure positioned outside the track edges, oralternatively, side shield layers can be positioned on opposite sides ofthe free layer structure and between the first and second shield layers.

The head described herein may form part of a GMR head, a CPP GMR sensor,a CPP tunnel valve sensor, etc. for use in a magnetic storage system.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is an air bearing surface view, not to scale, of a prior art spinvalve (SV) sensor.

FIG. 2 is an air bearing surface view, not to scale, of a prior artkeepered SV sensor.

FIG. 3 is a simplified drawing of a magnetic recording disk drivesystem.

FIG. 4 is a partial view of the slider and a merged magnetic head.

FIG. 5 is a partial ABS view, not to scale, of the slider taken alongplane 5-5 of

FIG. 4 to show the read and write elements of the merged magnetic head.

FIG. 6 is an enlarged isometric illustration, not to scale, of the readhead with a spin valve sensor.

FIG. 7 is an ABS illustration of a CPP GMR sensor, not to scale,according to an embodiment of the present invention.

FIG. 8 is an ABS illustration of a CPP GMR sensor, not to scale,according to another embodiment of the present invention.

FIG. 9 is an ABS illustration of a CPP GMR sensor, not to scale,according to an alternate embodiment of the present invention.

FIG. 10 is an ABS illustration of a CPP GMR sensor, not to scale,according to an yet another alternate embodiment of the presentinvention.

FIG. 11 is an ABS illustration of a CPP tunnel valve sensor, not toscale, according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

Referring now to FIG. 3, there is shown a disk drive 300 embodying thepresent invention. As shown in FIG. 3, at least one rotatable magneticdisk 312 is supported on a spindle 314 and rotated by a disk drive motor318. The magnetic recording on each disk is in the form of an annularpattern of concentric data tracks (not shown) on the disk 312.

At least one slider 313 is positioned near the disk 312, each slider 313supporting one or more magnetic read/write heads 321. As the disksrotate, slider 313 is moved radially in and out over disk surface 322 sothat heads 321 may access different tracks of the disk where desireddata are recorded. Each slider 313 is attached to an actuator arm 319 bymeans of a suspension 315. The suspension 315 provides a slight springforce which biases slider 313 against the disk surface 322. Eachactuator arm 319 is attached to an actuator means 327. The actuatormeans 327 as shown in FIG. 3 may be a voice coil motor (VCM). The VCMcomprises a coil movable within a fixed magnetic field, the directionand speed of the coil movements being controlled by the motor currentsignals supplied by controller 329.

During operation of the disk storage system, the rotation of disk 312generates an air bearing between slider 313 and disk surface 322 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 315 and supportsslider 313 off and slightly above the disk surface by a small,substantially constant spacing during normal operation.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 329, such asaccess control signals and internal clock signals. Typically, controlunit 329 comprises logic control circuits, storage means and amicroprocessor. The control unit 329 generates control signals tocontrol various system operations such as drive motor control signals online 323 and head position and seek control signals on line 328. Thecontrol signals on line 328 provide the desired current profiles tooptimally move and position slider 313 to the desired data track on disk312. Read and write signals are communicated to and from read/writeheads 321 by way of recording channel 325.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 3 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuators, and each actuator may support anumber of sliders.

FIG. 4 is a side cross-sectional elevation view of a merged magnetichead 400, which includes a write head portion 402 and a read headportion 404, the read head portion employing a dual spin valve sensor406 of the present invention. FIG. 5 is an ABS view of FIG. 4. The spinvalve sensor 406 is sandwiched between nonmagnetic electricallyinsulative first and second read gap layers 408 and 410, and the readgap layers are sandwiched between ferromagnetic first and second shieldlayers 412 and 414.

In response to external magnetic fields, the resistance of the spinvalve sensor 406 changes. A sense current (I_(s)) conducted through thesensor causes these resistance changes to be manifested as potentialchanges. These potential changes are then processed as readback signalsby the processing circuitry 329 shown in FIG. 3.

The write head portion 402 of the magnetic head 400 includes a coillayer 422 sandwiched between first and second insulation layers 416 and418. A third insulation layer 420 may be employed for planarizing thehead to eliminate ripples in the second insulation layer caused by thecoil layer 422. The first, second and third insulation layers arereferred to in the art as an “insulation stack”. The coil layer 422 andthe first, second and third insulation layers 416, 418 and 420 aresandwiched between first and second pole piece layers 424 and 426. Thefirst and second pole piece layers 424 and 426 are magnetically coupledat a back gap 428 and have first and second pole tips 430 and 432 whichare separated by a write gap layer 434 at the ABS. Since the secondshield layer 414 and the first pole piece layer 424 are a common layerthis head is known as a merged head. In a piggyback head an insulationlayer is located between a second shield layer and a first pole piecelayer. First and second solder connections (not shown) connect leads(not shown) from the spin valve sensor 406 to leads (not shown) on theslider 313 (FIG. 3), and third and fourth solder connections (not shown)connect leads (not shown) from the coil 422 to leads (not shown) on thesuspension.

FIG. 6 is an enlarged isometric ABS illustration of the read head 400shown in FIG. 4. The read head 400 includes the spin valve sensor 406.Insulating layers 602 and 604 flank the spin valve sensor. The spinvalve sensor 406 and the insulating layers 602 and 604 are locatedbetween electrically conductive first and second shield layers 408 and410.

The present invention provides a new sensor structure in which anin-stack bias structure provides both magnetostatic and exchange bias toa free layer structure, thereby providing an additive stabilizationscheme. This novel structure has been found to both increase thestability of the free layer structure and improve the stability of thein-stack bias structure. Many types of heads can use the structuredescribed herein, and the structure is particularly adapted to CPP GMRsensors and CPP tunnel valve sensors. In the following description, thetrack edges of the layers are defined by the track width (W). The sensorheight is in a direction into the face of the paper in an ABS view.Unless otherwise described, thicknesses of the individual layers aretaken perpendicular to the plane of the associated layer and areprovided by way of example only and may be larger and/or smaller thanthose listed. Similarly, the materials listed herein are provided by wayof example only, and one skilled in the art will understand that othermaterials may be used without straying from the spirit and scope of thepresent invention. The processes used to form the structures areconventional.

CPP GMR

FIG. 7 depicts an ABS view of a CPP GMR sensor 700 according to oneembodiment. “CPP” means that the sensing current (I_(s)) flows from oneshield to the other shield in a direction perpendicular to the plane ofthe layers forming the sensor 700.

As shown in FIG. 7, a first shield layer (S1) 702 is formed on asubstrate (not shown). The first shield layer 702 can be of any suitablematerial, such as permalloy (NiFe). An illustrative thickness of thefirst shield layer is in the range of about 0.5 to about 2 μm.

Seed layers (SEED) 704 are formed on the first shield layer 702. Theseed layers 704 aid in creating the proper growth structure of thelayers above them. Illustrative materials formed in a stack from thefirst shield layer 702 are a layer of Ta and a layer of NiFeCr.Illustrative thicknesses of these materials are Ta (30 Å) and NiFeCr (40Å). Note that the stack of seed layers 704 can be varied, and layers maybe added or omitted based on the desired processing parameters andoverall sensor design.

A multilayer in-stack bias structure 706 is formed above the seed layers704. The in-stack bias structure 706 includes an antiferromagnetic layer(AFM1) 708. A first bias layer (BL1) 710 is formed above theantiferromagnetic layer 708. A first antiparallel (AP) coupling layer(APC1) 712 is formed on the first bias layer 710. A second bias layer(BL2) 714 is formed above the first AP coupling layer 712. This magneticcoupling through the Ru spacer causes the bias layers 710, 714 to haveantiparallel-oriented magnetizations are pinned by an IrMnantiferromagnet.

Illustrative materials for the first and second bias layers 710, 714 areNiFe, CoFe₁₀ (90% Co, 10% Fe), CoFe₅₀ (50% Co, 50% Fe), NiFe/CoFe, etc.Illustrative thicknesses of the first and second bias layers 710, 714are between about 10 Å and 40 Å. A preferred material for the first APcoupling layer 712 is Ru. An illustrative thickness for the AP couplinglayer 712 is between about 4-15 Å, but is preferably selected to providea saturation field above about 10 KOe. Preferred materials for the AFMlayer 708 are PtMn, IrMn, etc. The thickness of the AFM layer 708 can beabout 60-150 Å if it is constructed from PtMn, and about 30-80 Å if itis constructed from IrMn A free layer structure 716 is formed above thein-stack bias structure 706. The magnetic orientation of the free layerstructure 716 must be preset during manufacture, otherwise theorientation will be unstable and could move around at random, resultingin a “scrambled” or noisy signal. This instability is a fundamentalproperty of magnetically soft materials, making them susceptible to anyexternal magnetic perturbations. Thus, the magnetic orientation of theactive area of the free layer structure 716 should be stabilized so thatwhen its magnetic orientation moves, it consistently moves around in asystematical manner rather than a random manner. The magneticorientation of the active portion of the free layer structure 716 shouldalso be stabilized so that it is less susceptible to reorientation,i.e., reversing. The overall structure disclosed herein stabilizes thefree layer structure 716.

A second AP coupling layer 717 is formed above the in-stack biasstructure. The significance of the second AP coupling layer (APC2) 717will soon be apparent.

As shown, the free layer structure 716 has first and second magneticfree layers (FL1), (FL2) 718, 720, respectively. The first and secondfree layers 718, 720 have differing magnetic thicknesses to provide areadable dR/R. Preferably, the second free layer 720 is thicker than thefirst free layer 718. The edges of the first and second free layers 718,720 define the track width W and are separated by a thin layer ofantiparallel coupling material (APC3) 722. The antiparallel couplinglayer 722 causes the magnetic orientations of the first and second freelayers 718, 720 in the free layer structure 716 to be orientedantiparallel to each other. The resulting free layer structure 716 canbe called a synthetic antiparallel coupled free layer structure.

The free layer structure 716 so can be designed to any desired magneticthickness. For example, suppose a free layer magnetic thickness of 30 Å(as shown) is desired. The first and second free layers 718, 720 wouldbe 60 Å and 30 Å thick. Because the first and second layers 718, 720 areAP coupled, the net magnetic thickness of the free layer structure 716is 30 Å. Illustrative materials for the first and second free layers718, 720 are NiFe, CoFe₁₀ (90% Co, 10% Fe), CoFe₅₀ (50% Co, 50% Fe),NiFe/CoFe, etc. The AP coupling layer 722 can be about 4-8 Å, and ispreferably selected to provide a saturation field above about 10 KOe.

As mentioned above, a typical prior art in-stack bias structure includesan antiferromagnetic (AFM) layer and one ferromagnetic bias layerthereon. That ferromagnetic layer stabilizes the free layer structure.However, the AFM coupling to the ferromagnetic layer is inverselyproportional to the thickness of the ferromagnetic layer. The problem isthat a single ferromagnetic layer must be as thick as the free layer inorder to provide sufficient stabilization. Such large thickness resultsin a poorly pinned ferromagnetic layer, and consequently, a poorlypinned in stack bias layer. Poor pinning of the ferromagnetic bias layerresults in a poorly stabilized free layer.

Thus, in a preferred embodiment, the first bias layer 710 has a magneticthickness that is greater than the magnetic thickness of the second biaslayer 714. By reducing the net magnetic thickness of the in-stack biasstructure, the pinning of the first bias layer 710 by the AFM layer 708is greatly improved over a single bias layer design. The strong pinningof the first bias layer 710 carries over to the second bias layer 714 byAP exchange coupling, thereby providing an in-stack bias structurehaving greatly improved stability. The improved pinning of the in-stackbias structure results in improved stability of the free layerstructure. A preferred net magnetic thickness of the in-stack biasstructure 706 is between about 0 and 20 Å, ideally about 10±5 Å. The APcoupling layer 712 is preferably about 4-8 Å thick.

As also described above, instead of using a typical spacer (e.g., Ta)between the in-stack bias structure 706 and free layer structure 716,the present invention implements an AP coupling layer 717 to create astabilizing AP exchange coupling between the second bias layer 714 ofthe in-stack bias structure 706 and the first free layer 718. Apreferred thickness of the second AP coupling layer 717 is about 16-18Å. Using an 18 Å thick Ru layer, for example, provides strong APexchange coupling (several hundred Oe), but not so much as to completelypin the first free layer 718.

Where the first bias layer 710 is larger than second bias layer 714(thereby providing a net magnetic moment), the in-stack bias layercreates a magnetostatic field that stabilizes the second free layer 720,supplementing the stabilizing effect of the AP exchange coupling betweenthe second bias layer 714 and the first free layer 718. Thus, thestabilizing effects of the magnetostatic and exchange bias are additive,providing overall greater stability to the free layer structure 716.

In the illustrative magnetic head shown in FIG. 7, the free layerdemagnetization field is calculated by the following equation:Free layer demagnetization field=4πM×(T _(FL) /W) Equation 1where:

M=free layer magnetic moment,

T_(FL)=free layer net magnetic thickness,

W=track width.

Where T_(FL)=30 Å and W=50 nm, the free layer demagnetization field is600 Oe. The exchange coupling across 18 Å of Ru=300 Oe. To cancel theremaining demagnetization of the free layer structure 716, the netthickness of the bias structure 706 need only be one half the netthickness of the free layer structure 716 to provide the remaining 300Oe stabilizing field. This is a great improvement over the prior art,where the bias layer thickness needed to be at least equal to the freelayer thickness. The net result is that the pinning of the first biaslayer 710 by the AFM 708 can be at least twice that of the prior art. Ofcourse, the thicknesses of the various layers will vary depending on thedesign chosen.

One skilled in the art will also note that for free layers having smallnet magnetic moments, the AP coupling between the bias structure 706 andthe free layer structure 716 may be sufficient. In such a situation, thenet moment of bias structure 706 can be reduced towards 0, relyingmainly on exchange coupling for stabilizing the free layer structure716. However, the preferred net moment of the bias structure 706 is 10±5Å.

With continued reference to FIG. 7, a first spacer layer (SP1) 723 isformed above the free layer structure 716. Illustrative materials forthe first spacer layer 723 include Cu, CuO_(x), Cu/CoFeO_(x)/Cu stack,etc. The first spacer layer 723 can be about 10-40 Å thick, preferablyabout 30 Å.

Then an antiparallel (AP) pinned layer structure 724 is formed above thefirst spacer layer 723. As shown in FIG. 7, first and second AP pinnedmagnetic layers, (AP1) and (AP2) 726, 728, are separated by a thin layerof an antiparallel coupling material (APC4) 730 such that the magneticmoments of the AP pinned layers 726, 728 are self-pinned antiparallel toeach other.

In the embodiment shown in FIG. 7, the preferred magnetic orientation ofthe pinned layers 726, 728 is for the first pinned layer 726, into theface of the structure depicted (perpendicular to the ABS of the sensor700), and out of the face for the second pinned layer 728. Illustrativematerials for the pinned layers 726, 728 are CoFe₁₀ (90% Co, 10% Fe),CoFe₅₀ (50% Co, 50% Fe), etc. separated by a Ru layer 730. Illustrativethicknesses of the first and second pinned layers 726, 728 are betweenabout 10 Å and 25 Å. The Ru layer 730 can be about 4-8 Å, but ispreferably selected to provide a saturation fields above about 10 KOe.In a preferred embodiment, each of the pinned layers 726, 728 is about20 Å with an Ru layer 730 therebetween of about 4 Å.

A cap (CAP) 732 is formed above the AP pinned layer structure 724.Exemplary materials for the cap 732 are Ta, Ta/Ru stack, etc. Anillustrative thickness of the cap 732 is 20-30 Å.

A second shield layer (S2) 734 is formed above the cap 728. Aninsulative material 732 such as Al₂O₃ is formed on both sides of thesensor stack.

FIG. 8 depicts an ABS view of a CPP GMR sensor 800 according to anotherembodiment. The CPP GMR sensor 800 generally has the same configurationas the structure shown in FIG. 7, except that an AFM layer 802 has beenadded between the AP pinned layer structure 724 and the cap 732. The AFMlayer 802 pins the AP pinned layer structure 724.

Note that if there is no upper AFM layer 802 at the top of the sensorstack, the designer has more freedom to select materials for the AFMlayer 708 at the bottom of the sensor stack. For instance, PtMn can beused for the lower AFM layer 708 if no upper AFM layer 802 is present.But if PtMn is used for the upper AFM layer 802, and the pinned layers726, 728 are oriented into and out of page, when a high temperature isused to set the pinned layers 726, 728, a different AFM material isrequired for the lower AFM layer 708. Accordingly, IrMn can be used toform the lower AFM layer 708 and set the orientations of the bias layers710, 714 at a lower temp.

FIG. 9 depicts an ABS view of a CPP GMR sensor 900 according to anotherembodiment. The CPP GMR sensor 900 generally has the same configurationas the structure shown in FIG. 7, except that the second shield layer734 extends downwardly so that it is positioned along a portion of thesensor stack. This design provides better track resolution, because thesecond shield layer 734 is closer to the free layer structure 716.Magnetic fields from adjacent tracks are drawn to the second shieldlayer 734, and therefore are less likely to interfere with the readingfunction.

FIG. 10 depicts an ABS view of a CPP GMR sensor 1000 according toanother embodiment. The CPP GMR sensor 1000 generally has the sameconfiguration as the structure shown in FIG. 7, except that side shieldlayers 1002, 1004 extend downwardly so that they positioned along aportion of the sensor stack. Like the structure shown in FIG. 9, thisdesign provides better track resolution, because the side shield layers1002, 1004 are closer to the free layer structure 716. Magnetic fieldsfrom adjacent tracks are drawn to the side shield layers 1002, 1004, andtherefore are less likely to interfere with the reading function.

CPP Tunnel Valve

FIG. 11 depicts an ABS view of a CPP tunnel valve sensor 1100 accordingto one embodiment. The CPP tunnel valve sensor 1100 generally has thesame configuration as the structure shown in FIG. 7, except that thefirst spacer layer 723 is formed of a dielectric barrier material, suchas, Al₂O₃, AlO_(x), MgO_(x), etc. The first spacer layer 723 is verythin such that the electric current passing through the sensor 1100“tunnels” through the first spacer layer 723. An illustrative thicknessof the first spacer layer 723 is 3-6 Å.

In one method to fabricate the sensors shown in FIGS. 7-11, the layers702-732 (and optionally AFM layer 802) are formed. A resist mask isformed on the cap layer 732 to cover and define the track width W. Thestructure is etched or milled down to the seed layers 704 or the firstshield layer 702. The structure areas outside the track edges are thenfilled with Al₂O₃ 750 or other electrically insulative material. Sideshield layers 1002, 1004 can be added by conventional methods. Thestructure is planarized via chemical-mechanical polishing (CMP). Thenthe second shield layer 734 is formed.

Another method to fabricate the sensors shown in FIGS. 7-11 is to formthe first shield layer 702 and optionally the seed layers 704. A resistmask is formed outside the desired track edges, leaving the track widthW exposed. The remaining layers 708-732 (and optionally layer 802) areformed in the track width W defined between the mask edges. The resistis removed. The structure areas outside the track edges are then filledwith Al₂O₃ 750 or other electrically insulative material. Side shieldlayers 1002, 1004 can be added by conventional methods. The structure isplanarized via chemical-mechanical polishing (CMP). Then the secondshield layer 734 is formed.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. For example, the structures and methodologies presentedherein are generic in their application to all MR heads, AMR heads, GMRheads, TMR heads, CPP GMR heads, etc. Thus, the breadth and scope of apreferred embodiment should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

1. A magnetic head, comprising: an in-stack bias structure, comprisingan antiferromagnetic layer; a first bias layer positioned towards theantiferromagnetic layer, a magnetic moment of the first bias layer beingpinned by the antiferromagnetic layer; a first antiparallel couplinglayer positioned adjacent the first bias layer; and a second bias layerpositioned between the first and second antiparallel coupling layers andhaving a magnetic moment pinned antiparallel to the magnetic moment ofthe first bias layer; a second antiparallel coupling layer positionedadjacent the second bias layer of the bias structure; and a free layerstructure positioned adjacent the antiparallel coupling layer,comprising: a first free layer having a magnetic moment; and a secondfree layer having a magnetic moment pinned antiparallel to the magneticmoment of the first free layer; wherein the second bias layer isantiparallel coupled to the first free layer of the free layer structurefor stabilizing the free layer structure.
 2. A head as recited in claim1, wherein a net magnetic thickness of the first and second bias layersis greater than zero for providing magnetostatic stabilization of thefree layer structure.
 3. A head as recited in claim 2, wherein the netmagnetic thickness of the first and second bias layers is less thanabout 20 Å.
 4. A head as recited in claim 1, wherein the first biaslayer has a larger magnetic thickness than the second bias layer.
 5. Ahead as recited in claim 1, wherein a thickness of the secondantiparallel coupling layer is about 16 Å to about 20 Å.
 6. A head asrecited in claim 1, wherein a thickness of the second antiparallelcoupling layer is greater than a thickness of the first antiparallelcoupling layer.
 7. A head as recited in claim 1, wherein the second freelayer has a larger magnetic thickness than the first free layer.
 8. Ahead as recited in claim 1, further comprising an antiparallel pinnedlayer structure positioned towards the free layer structure on anopposite side of the free layer structure relative to the biasstructure, the antiparallel pinned layer structure having at least twopinned layers having magnetic moments that are self-pinned antiparallelto each other.
 9. A head as recited in claim 8, further comprising asecond antiferromagnetic layer positioned towards the antiparallelpinned layer structure.
 10. A head as recited in claim 1, furthercomprising a shield layer positioned above the free layer structure,portions of the shield layer positioned outside track edges of the freelayer structure extending downwardly, flanking the track edges of thefree layer structure.
 11. A head as recited in claim 1, furthercomprising a first shield layer positioned below the in-stack biasstructure, a second shield layer positioned above the free layerstructure, and side shield layers positioned on opposite sides of thefree layer structure and between the first and second shield layers. 12.A head as recited in claim 1, wherein the head forms part of a CPP GMRsensor.
 13. A head as recited in claim 1, wherein the head forms part ofa tunnel valve sensor.
 14. A magnetic head, comprising: an in-stack biasstructure, comprising an antiferromagnetic layer; a first bias layerpositioned towards the antiferromagnetic layer, a magnetic moment of thefirst bias layer being pinned by the antiferromagnetic layer; a firstantiparallel coupling layer positioned adjacent the first bias layer;and a second bias layer positioned between the first and secondantiparallel coupling layers and having a magnetic moment pinnedantiparallel to the magnetic moment of the first bias layer; a secondantiparallel coupling layer positioned adjacent the second bias layer ofthe bias structure; a free layer structure positioned adjacent theantiparallel coupling layer, comprising: a first free layer having amagnetic moment; and a second free layer having a magnetic moment pinnedantiparallel to the magnetic moment of the first free layer; and anantiparallel pinned layer structure positioned towards the free layerstructure on an opposite side of the free layer structure relative tothe bias structure, the antiparallel pinned layer structure having atleast two pinned layers having magnetic moments that are self-pinnedantiparallel to each other; wherein the second bias layer isantiparallel coupled to the first free layer of the free layer structurefor stabilizing the free layer structure.
 15. A head as recited in claim14, wherein a net magnetic thickness of the first and second bias layersis greater than zero for providing magnetostatic stabilization of thefree layer structure.
 16. A head as recited in claim 15, wherein the netmagnetic thickness of the first and second bias layers is less thanabout 20 Å.
 17. A head as recited in claim 14, wherein the first biaslayer has a larger magnetic thickness than the second bias layer.
 18. Ahead as recited in claim 14, wherein a thickness of the secondantiparallel coupling layer is about 16 Å to about 20 Å.
 19. A head asrecited in claim 14, wherein a thickness of the second antiparallelcoupling layer is greater than a thickness of the first antiparallelcoupling layer.
 20. A head as recited in claim 14, wherein the secondfree layer has a larger magnetic thickness than the first free layer.21. A head as recited in claim 14, further comprising a secondantiferromagnetic layer positioned towards the antiparallel pinned layerstructure.
 22. A head as recited in claim 14, further comprising ashield layer positioned above the free layer structure, portions of theshield layer positioned outside track edges of the free layer structureextending downwardly, flanking the track edges of the free layerstructure.
 23. A head as recited in claim 14, further comprising a firstshield layer positioned below the in-stack bias structure, a secondshield layer positioned above the free layer structure, and side shieldlayers positioned on opposite sides of the free layer structure andbetween the first and second shield layers.
 24. A head as recited inclaim 14, wherein the head forms part of a CPP GMR sensor.
 25. A head asrecited in claim 14, wherein the head forms part of a tunnel valvesensor.
 26. A magnetic head, comprising: an in-stack bias structure,comprising an antiferromagnetic layer; a first bias layer positionedtowards the antiferromagnetic layer, a magnetic moment of the first biaslayer being pinned by the antiferromagnetic layer; a first antiparallelcoupling layer positioned adjacent the first bias layer; and a secondbias layer positioned between the first and second antiparallel couplinglayers and having a magnetic moment pinned antiparallel to the magneticmoment of the first bias layer; a second antiparallel coupling layerpositioned adjacent the second bias layer of the bias structure; a freelayer structure positioned adjacent the antiparallel coupling layer,comprising: a first free layer having a magnetic moment; and a secondfree layer having a magnetic moment pinned antiparallel to the magneticmoment of the first free layer; and an antiparallel pinned layerstructure positioned towards the free layer structure on an oppositeside of the free layer structure relative to the bias structure, theantiparallel pinned layer structure having at least two pinned layershaving magnetic moments that are self-pinned antiparallel to each other;wherein the second bias layer is antiparallel coupled to the first freelayer of the free layer structure for stabilizing the free layerstructure; wherein a net magnetic thickness of the first and second biaslayers is greater than zero for providing magnetostatic stabilization ofthe free layer structure.
 27. A magnetic storage system, comprising:magnetic media; at least one head for reading from and writing to themagnetic media, each head having: a sensor having the structure recitedin claim 1; a write element coupled to the sensor; a slider forsupporting the head; and a control unit coupled to the head forcontrolling operation of the head.
 28. A magnetic storage system,comprising: magnetic media; at least one head for reading from andwriting to the magnetic media, each head having: a sensor having thestructure recited in claim 14; a write element coupled to the sensor; aslider for supporting the head; and a control unit coupled to the headfor controlling operation of the head.
 29. A magnetic storage system,comprising: magnetic media; at least one head for reading from andwriting to the magnetic media, each head having: a sensor having thestructure recited in claim 26; a write element coupled to the sensor; aslider for supporting the head; and a control unit coupled to the headfor controlling operation of the head.